1. Field of the Invention
The present invention relates to a spanning tree system, and more particularly to a spanning tree system, a spanning tree configuration node, a spanning tree configuration method, and its program capable of connecting the trees without causing a loop of path, in dividing a spanning tree into domains.
2. Description of the Related Art
Hitherto, this kind of spanning tree is used to prevent from data loops, by forming such a tree link as assuming that a loop does not exist logically even in the case where a loop ring physically exists in a network.
As the conventional technique about the spanning tree, there exist the following examples.
For example, in the standard documents (non-patent article 1) issued by the IEEE, titled as “IEEE•Standard•802.1D (IEEE Std 802.1D), 1998”, when a loop (ring) exists in a network, in order to prevent from data loops, a control method called a spanning tree is defined (hereinafter, referred to as the non-patent article 1), in which method the control information called as the Bridge Protocol Data Unit (BPDU) is exchanged between nodes, and one portion of the physical loop network is disabled, hence to form the logical tree topology.
Further, in the standard documents (non-patent article 2) issued by the IEEE, titled as “IEEE•Standard•802.1W (IEEE Std 802.1W), 2001”, a control method called a high-speed spanning tree is defined (hereinafter, referred to as the non-patent article 2), in which the tree configuration in the conventional technique 1 is speeded up by expanding the exchange method of the control information, and further, a detour path can be set promptly at an occurrence of a failure, by previously setting the detour path.
The paper titled as “Institute of Electronics, Information and Communication Engineers, Society Meeting 2002, B-7-11 to B-7-13, Proposal of Ethernet Architecture GOE (Global Optical Ethernet) for Future Generation”, describes a method of transferring the Ethernet frame, with an identification tag indicating the destination information and the like inserted into the Ethernet frame and with a forwarding table configured by using the spanning tree created in a multiphasic way (hereinafter, referred to as the non-patent article 3).
One example of the spanning trees configured in the non-patent articles 1 to 3 is shown in FIG. 29. The created spanning tree is indicated by the heavy line in FIG. 29. In this conventional spanning tree configured for a network, one spanning tree is configured on the whole network while the node 11 to the node 32 exchange the control frames (information) with each other.
The above conventional technique, however, has the following problems.
At first, in any convention technique, it takes a long time to configure the spanning tree.
In the technique of the non-patent article 1, although the spanning tree is configured by exchanging the control frame called BPDU frame, when performing a state transition, each node confirms arrival of a new BPDU frame and therefore, performs a state transition by using a timer. According as the number of the nodes to be accommodated in a network increases, it takes a longer time to configure the spanning tree.
The number of the BPDU frames exchanged between each node increases according to an increase in the number of the bridge nodes belonging to a network. Therefore, configuration of the spanning tree takes the longer time according to an increase in the size of the network.
The technique of the non-patent article 2 is identical to the conventional technique 1 in that the spanning tree is configured by exchange of the control frame called BPDU frame, and it, however, speeds up the state transition, by exchange of a confirmation frame called Proposal and Agreement. Therefore, compared with the non-patent article 1, the technique of the non-patent article 2 can shorten the configuration time of the spanning tree, but complicate the shape of the topology and therefore, it takes the longer time to configure the spanning tree, according to an increase in the number of the nodes to be accommodated into a network.
In the technique of the non-patent article 3, since the spanning tree configured by using the method of the non-patent article 2 is created in a multiphasic way, configuration of the spanning tree takes the longer time for the same reason as the non-patent article 2.
At second, in any conventional technique, there is such a problem that at occurrence of a failure, it affects a large area.
In the conventional technique of the non-patent article 1, in the case of changing the configuration of the spanning tree owing to a failure, the ports on the whole network are once closed and then the spanning tree has to be reconfigured.
In the conventional technique of the non-patent article 2, in the case of changing the configuration of the spanning tree owing to a failure, one of the network is locally stopped, the configuration is gradually changed, and then the spanning tree on the whole network is reconfigured. Therefore, even in a place distant from a failure, at last it is necessary to stop the network temporarily.
In the conventional technique of the non-patent article 3, since the spanning tree configured by using the method of the non-patent article 2 is created in a multiphasic way, there is such a problem that at occurrence of a failure, it affects a large area, owing to the same reason as the non-patent article 2.
In the above-mentioned conventional technique 1 to the conventional technique 3, since only one node that is a connecting point to connect the existing network can be provided, in order to prevent the spanning tree from being a loop shape, it is difficult to configure the spanning tree in every network.